A fast and efficient method for installing small diameter flowlines offshore is by means of reel, tensioner, and straightener devices mounted on a floating vessel. However, this "pipe reel" method becomes awkward if multiple lines must be laid simultaneously, as is often the case for flowlines laid to, or originating at, seafloor wellheads. A typical flowline bundle to such a subsea well consists of two 3-inch I.D. production flowlines, one 2-inch I.D. annulus access line, one 1-inch I.D. chemical injection line, one 1-inch I.D. hydraulic power line and one 2-inch O.D. chemical control cable. For such multiple lines it becomes necessary to spool each line onto a separate reel, and then either (1) lay each line separately off the floating vessel while carefully monitoring each suspended span, or (2) bring the separate lines together and wrap them with tape to form a "flowline bundle" which is then laid into the water as a single entity.
Problems frequently are encountered with multiple flowlines or flowline bundles as they are being laid or as they are being pulled-in and connected, either to a subsea wellhead or other subsea structure, or into a J-tube conduit on a fixed platform. Potential problems include dynamic impacts between the lines during pipelaying if laid separately. For a pull-in of a flowline bundle to a subsea wellhead or other subsea structure, potential problems include lateral buckling of the smaller lines due to bending of the bundle, overstressing of some of the lines because of non-uniform sharing of the tension and bending loads, and large torque required to orient the flowline terminal head before attaching to the wellhead. For a flowline bundle pulled into a J-tube, potential problems include increased pullforce due to composite-beam bending effect for pipes that are tightly wrapped, differential stretching or buckling of the smaller lines inside the curved portion of the J-tube, or formation of buckled pipe "loops" at the mouth of the J-tube, for bundles that are only loosely or partially wrapped. The present invention is directed toward overcoming these and other problems of the art as will be apparent hereinafter.
Relevant prior art includes a report by Kvarner Subsea Contracting A/S, and U.S. Pat. Nos. 2,832,374; 3,197,953; 3,526,086; 607,932.